linux-kernel - Re: [PATCH v2 09/35] entry/kvm: handle lazy rescheduling at guest-entry

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Message-ID: <20240528161316.GE26599@noisy.programming.kicks-ass.net>
Date: Tue, 28 May 2024 18:13:16 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Ankur Arora <ankur.a.arora@...cle.com>
Cc: linux-kernel@...r.kernel.org, tglx@...utronix.de,
	torvalds@...ux-foundation.org, paulmck@...nel.org,
	rostedt@...dmis.org, mark.rutland@....com, juri.lelli@...hat.com,
	joel@...lfernandes.org, raghavendra.kt@....com,
	sshegde@...ux.ibm.com, boris.ostrovsky@...cle.com,
	konrad.wilk@...cle.com, Paolo Bonzini <pbonzini@...hat.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v2 09/35] entry/kvm: handle lazy rescheduling at
 guest-entry

On Mon, May 27, 2024 at 05:34:55PM -0700, Ankur Arora wrote:
> Archs defining CONFIG_KVM_XFER_TO_GUEST_WORK call
> xfer_to_guest_mode_handle_work() from various KVM vcpu-run
> loops to check for any task work including rescheduling.
> 
> Handle TIF_NEED_RESCHED_LAZY alongside TIF_NEED_RESCHED.
> 
> Also, while at it, remove the explicit check for need_resched() in
> the exit condition as that is already covered in the loop condition.
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Andy Lutomirski <luto@...nel.org>
> Originally-by: Thomas Gleixner <tglx@...utronix.de>
> Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/
> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
> ---
>  include/linux/entry-kvm.h | 2 +-
>  kernel/entry/kvm.c        | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/entry-kvm.h b/include/linux/entry-kvm.h
> index 6813171afccb..674a622c91be 100644
> --- a/include/linux/entry-kvm.h
> +++ b/include/linux/entry-kvm.h
> @@ -18,7 +18,7 @@
>  
>  #define XFER_TO_GUEST_MODE_WORK						\
>  	(_TIF_NEED_RESCHED | _TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL |	\
> -	 _TIF_NOTIFY_RESUME | ARCH_XFER_TO_GUEST_MODE_WORK)
> +	 _TIF_NOTIFY_RESUME | _TIF_NEED_RESCHED_LAZY | ARCH_XFER_TO_GUEST_MODE_WORK)

Same as last patch, it seems weird to have both RESCHED flags so far
apart.